The present invention relates to a battery status or power condition indicator for a single battery used as a power source and more particularly to a system for determining the status or power condition of each battery and/or the condition of the related cable supply system connecting the batteries to the load in a multi-battery series power pack.
Power or work demands can be made upon battery power packs that have weak cells or batteries and/or high resistance cables without showing a noticeable loss in power output. This is especially true in devices that vary the voltage input to the load to control the speed or rate of work being done. This deficiency can go undetected and eventually cause a total failure of the battery pack. This type of failure can also occur in devices that apply the total pack output directly to the load. In any case, early detection of a power supply system defect will result in major savings in battery costs and as well as less down-time of equipment.
An example of a machine which is operated by a multi-battery pack is a typical electric golf cart. Such a golf cart may be powered by a battery pack comprising a series string of six-volt batteries of a type generally similar to an automobile battery. When the batteries are in a charged state and fully charged, each battery exhibits a voltage across its terminals of about 6.1 volts DC. This voltage drops slightly during peak loads. As the charge is gradually reduced in normal service, the terminal voltage tends to remain constant at about six volts, with a rapid drop towards zero as the battery becomes completely discharged.
Abnormally low terminal voltage of a battery or cell ordinarily indicates a very low charge condition, an extremely high level of loading or a defective cell. If one battery in a series of batteries, all of which have received the same maintenance and charge, has low terminal voltage, this is an indication of a faulty battery or a defective cable within the power supply system.
U.S. Pat. No. 4,198,597 issued to Sawyer discloses a detector for sensing a defective cell among a plurality of voltage-producing cells which together form a source of DC electrical power. When a cell becomes defective causing its voltage output to drop, the voltage produced by the remaining cells create a load current by which the defective cell goes negative and forward biases the corresponding light-emitting diode which emits light and identifies the defective cell. Such a device, however, is not reliable in a situation where the light emitting diode is defective or there is a malfunction or problem with other portions of the circuitry. In such a situation, even though a battery may be defective, the corresponding light-emitting diode will not light up to indicate a defective cell.
It is therefore a principal object of the present invention to provide a system for indicating the condition of each cell of a multi-battery battery pack and/or to isolate a defective cable connecting the batteries to the load.
A further object of the present invention is to provide a system for monitoring the condition of a plurality of batteries in a multi-battery battery pack which is simple in design, reliable and inexpensive to manufacture.
Still another object of the present invention is to provide a condition monitor for each battery in a multi-battery battery pack which is powered by the battery pack and "remembers" that condition after the load is removed even though the battery voltage rises after the load is removed.